Liquid crystal displays (LCDs) are dominant in the flat panel display market, accounting for more than 100 billion US dollars annually. State-of-the-art LCDs in large volume production use optical anisotropic, or birefringent, liquid crystals. They are operated between a bright and a dark state, or in any state between these states. In both the bright and dark states, the liquid crystal material is optically anisotropic but the optical axes are in different directions. One of the major problems with the LCDs is that in the dark state the liquid crystal material is in the anisotropic state. In this state, there is residual optical retardation at the off-axis viewing angles, causing light leakage at these viewing angles. The light leakage severely limits the viewing angle and contrast ratio of the LCDs.
A more recent LCD is the polymer stabilized blue phase (PB) LCD. In the PB-LCD dark state, the liquid crystal material is in the optical isotropic blue phase. This LCD experiences no residual optical retardation at off-axis viewing angles, and therefore the PB-LCD has a good viewing angle. Nonetheless, the PB-LCD exhibits continuing problems. One such problem is that the blue phases are exhibited by chiral liquid crystals. Without dispersed polymers, the blue phases usually exist in a very narrow temperature region, around 1 degree or less. In order to use the blue phases in display applications, polymer stabilization is employed to widen the temperature of the blue phase. The polymer stabilization is achieved by mixing the liquid crystal with a small amount of monomer (or oligomer) and polymerizing the monomer in the blue phase. During the polymerization, the temperature must be precisely controlled so that the mixture is in the blue phase. This is a problem in manufacturing PB-LCD. The blue phase possesses a cubic structure. It is difficult to manufacture large size display with uniform optical state. This is another problem in manufacturing PB-LCD.
Advantageously, the present invention overcomes the foregoing problems by providing polymer stabilized isotropic (PSI) liquid crystals. These PSI liquid crystals can be used for displays and as phase modulators, and exhibit many technical merits, such as providing a large viewing angle, fast response time, and enhanced contrast ratio. In addition, the PSI liquid crystals of the present invention are easy to manufacture as large size displays, such displays exhibiting improved dark state. Further, they are amenable to an easy manufacturing process having a wider temperature range. Finally, the PSI phase modulator of the present invention exhibits polarization-insensitivity. These attributes, among others, are found in the PSI liquid crystals according to the present invention.